Akintorinwa and Adesoji

7/28/2019 Akintorinwa and Adesoji

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International Journal of Physical Sciences Vol. 4 (8), pp. 443-454, August, 2009Available online at http://www.academicjournals.org/IJPSISSN 1992 - 1950 2009 Academic Journals

Full Length Research Paper

Application of geophysical and geotechnical

investigations in engineering site evaluationO. J. Akintorinwa* and J. I. Adesoji

Department of Applied Geophysics, Federal University of Technology, P.M.B. 704, Akure. Nigeria.

Accepted 08 July, 2009

Geophysical and geotechnical studies were conducted at a proposed Switch station facility forTelecommunication at a site in the south-eastern part of Nigeria. The aim of the study is to evaluate thesub-soil conditions and electrical properties of the soil which may have effect on the proposed mastand switch facilities system. The geophysical investigation involved the Vertical Electrical Sounding(VES) technique using the Schlumberger configuration and a geotechnical investigation. A total of

sixteen (16) VES stations were occupied within the study site. The geotechnical study involvedBoreholes drilling as well as Cone Penetration Tests (CPT). A total of six (6) CPTs and three (3)Boreholes drilling were utilised within the study area. This was done to provide controls on thegeophysical interpretation. Four subsurface layers were delineated within the study area which include:the topsoil (mixture of sand, silt and clay), coarse sand, clayey sand and sand. This correlated with thesub-soil investigation. The study area is underlain by a stratum of medium stiff to stiff lateriticclayey/silty sand to the depth of about 20 m as explored by the Borehole. The choice of foundationconstruction for the proposed structure must take care of the settlement characteristics of the clayeymaterial. The subsurface layers up to a depth of 5 m is of moderate to high resistivity values (> 180ohm-m) and it may not serve as a good electric earthing material, therefore there is a need to improvethe subsurface conductivity of this layer most especially within the area where the electrode for theearthling system will be buried.

Key words: Vertical electrical sounding, conductivity, cone penetration test, earthing, settlement characteristic.

INTRODUCTION

With the growing demand for space utilization, there arealso an increasing number of incidences of structuraldamages which can be accompanied by collateral losses.Uncertainties associated with the design and planning ofstructures play a role in such failures. Design uncertain-ties related to unknown soil properties are among themost important (Bremmer, 1999). The non linearbehaviour of soil under stress, the difficulty in estimating

soil properties in undisturbed or in-situ conditions, andhigh spatial variability, all make it impossible to predictthe exact behaviour of soil in time and space. Thesedifficulties call for safety factor to ensure an adequatemargin against unexpected deviations in the predictedsituation.

Different approaches are commonly used in other toascertain the in-situgeo-mechanical properties of the soil;

*Corresponding author. E-mail: [email protected].

i) The use of Geophysical Techniques, such as electricaresistivity method (VES) or seismic method.ii) Direct probing using static or dynamic penetrationtechniques and or boreholes.

The success in the applicability of geophysical techni-ques depends on so many factors. The most important isthe existence of a significant and detectable contrasbetween the physical properties of the different units inthe subsurface, such as velocity, electrical resistivityconductivity, density, acoustic properties, subsurfacegeology and the environmental conditions. Penetrationdevices produce little overall disturbance in the soil. Themost widely used static and dynamic penetration test arethe Cone Penetration Test CPT (for soft soils) and theStandard Penetration Test SPT (for relatively hard soils)(Baldi et al., 1995).

For CPT, a cone at the end of a series of rods ispushed into the ground at a constant rate, and measure-ments are made of the resistance to the penetration of


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444 Int. J. Phys. Sci.

the cone. This is known as cone resistance or qc, whichis the total force (Qc) acting on the cone divided by theprojected area (Ac) of the cone. The cone resistance qc isa direct indicator of the strength of the soil at a givendepth. Cost, efficiency, speed, simplicity, reliability, andthe ability to provide near continuous information on the

soil properties with depth are the important reasons forthe increasing popularity of CPT. The primary signify-cance of CPT comes from the fact that it represents aminiature driven pile or foundation in soil; hence, the pilebearing capacity (pressure between a foundation and thesoil which will produce shear failure in the soil) can bedirectly estimated from qc. Thus, CPT provides valuableconstraints for all settlement and stability calculations.CPT qc responds to soil changes within five to ten timesthe cone diameter (standard = 35.6 mm) above andbelow the cone. Although CPT provides valuable infor-mation as to the strength of the soil, the information isrestricted to the CPT location (Eslaamizaad et al., 1998).CPTs are commonly performed tens or hundreds ofmeters apart. Soil models based on lateral interpolationof CPT data collected at a few locations at a given siteobviously contain large uncertainties, increasing the riskin engineering design. The aims and objectives of thestudy are:

1. To delineate the subsurface geological sequence anddetermine the geoelectric parameter.2. To identify existing subsurface geologic features suchas faults, sinkholes and cavities in an area prone tosubsidence and geologic instabilities.3. To determine from soil resistivity measurements, thenature of the soil and its suitability as an electrical system

earthing medium.4. To determine the geotechnical and nature of the studyarea.5. To evaluate from the above the suitability of thesubsurface soil within the study area for the proposedcommunication mast system.

Geomorphology/Climate/Vegetation/Geology of thestudy area

The area is in the coastal region of Nigeria and theelevation is of low lying with elevation of not more than 3

m above the sea level. The Nigeria coastal zone is withinthe tropical climate areas. The rainy season is April toNovember and dry season is in December to march. Thearea has an annual rainfall varies between 1,500 and4,000mm (Ibe, 1988). During the rainy season, windspeed increases to about 10 m/s especially during heavyrainfalls and thunderstorms. Temperature in the coastalarea is modulated by the cloud cover and by the damp air.However, the mean monthly temperature vary between24 and 32

oC. Mangrove and rain forests characterize the

vegetation of the study area.The study area is located within the Niger Delta basin

which is a major geomorphic feature in the Nigeriacoastal zone. The evolution of the modern Niger Deltastarted in the Early Tertiary with sediments being sup-plied by the Niger Benue river system which over theyears have built-up a large Delta. The Niger Delta complex consists of sedimentary formations deposited in a

high-energy deltaic environment. Sediment built up wasaccompanied by growth faulting normal to the direction ofpropagation of the progradation which resulted in a seriesof near parallel faults bounded by the depositional beltThese depobelts are successively younger from north tosouth. Overlying these depobelts is the stratigraphicsequence that consists of three sedimentary units (BeninFormation, Agbada Formation and Akata Formation).The Benin Formation is described as Coastal plainsands. It consists mainly of sand and gravels with thick-nesses that can reach 2,100 m (Avbovbo, 1978). Thesands and sandstones are coarse to fine granular intexture and can be unconsolidated. The Agbada Formation consists mainly of sands, sandstones and siltstonesThe sandstones or sands are very coarse to fine grainedThey are often poorly sorted except where sand gradesinto shale. The Akata Formation is the major basal unit inthe Niger Delta Complex. This is a marine pro-deltamegafacies, comprising mainly of shales with occasionaturbidite sandstones and siltstones.

METHODOLOGY

Geophysical survey

Sixteen (16) vertical electrical soundings were conducted within thestudy area (Figure 1) using an ABEM-SAS 300C TerrameterSchlumberger array was employed with electrode separations (ABranging from 2 to 1000 m. The location of each sounding stationwas recorded in Universal Traverse Mercator (UTM) coordinateswith the aid of a GARMIN 12 channel personal navigator (GPS) uniThe soundings were performed parallel to the traverse lines and theapparent resistivity values were calculated.

The apparent resistivity measurements at each station wereplotted against electrode spacing (AB/2) on bi-logarithmic graphsheets. The curves were inspected to determine the number andnature of the layering. Partial curve matching was carried out for thequantitative interpretation of the curves. The results of the curvematching (layer resistivities and thicknesses) were fed into thecomputer as a starting model in an iterative forward modelingtechnique using RESIST version 1.0 (Vander Velper, 1988). Fromthe interpretation results (layer resistivities and thicknesses)

geoelectric sections along directions (N-S and E-W) were producedand results were also used to generate maps and layer parametehistograms.

Geotechnical survey

Cone Penetration tests were performed at a total of six (6) locationswithin the study area (Figure 1). The tests were carried out to adepth of 20 m. The Dutch static penetration measures theresistance of penetration into soils using a 60o steel cone with anarea of 10.2 cm2. The cone penetrometer test is a means oascertaining the resistance of the soil. The layer sequences are


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Akintorinwa and Adesoji 445

Figure 1. Data Acquisition Map of the Study Area showing the Vertical Electrical Sounding(VES) Stations and the Geotechnical Sampling Points.

interpreted from the variation of the values of the cone resistancewith depth. The test is carried out by securing the winch frame tothe ground by means of anchors. These anchors provided thenecessary power to push the cone into the ground. The cone andthe tube are pushed together into the ground for 20 to 25 cm; thecone is pushed ahead of the tube for 3.5 cm at a uniform rate ofabout 2 cm/sec. The resistance to the penetration of the coneregistered on the pressure gauge connected to the pressurecapsule is recorded. The tube is then pushed down and theprocedure described above repeated. From the series of recordedgauge readings, cone resistance and sleeve friction are plottedagainst depth. Three boreholes were drilled within the study area(Figure 1) undisturbed samples at various locations were taken at

appropriate intervals using a specially designed 60.5 mm internaldiameter U Type sampler. The sampler is fitted with a cutter at theopen end and a waste barrel at the other end. A round steel ball inthe driving head of the sampler permits the escape of air and wateras the sample enters the tube. The diameter of the sample tube is25 mm and lined with 60.5 mm plastic tube. The samples aretrimmed to the desired length and usually 15 cm covered in aplastic tube. An identification label is attached. The numbers ofblows required to drive the sample 15 cm into the ground isrecorded. Sometimes, the regular U4 sampler is used to recover theundisturbed samples.

The in situ Standard Penetration Test (SPT) was carried out,usually in the non-cohesive strata. The standard penetration test

consists of driving a thick walled 50 mm diameter steel tube into thesand at the bottom of each borehole by means of a 63.5 kghammer dropping 75cm. The number of blows required to drive thetube 30 cm after an initial penetration of 15 cm is recorded as theSPT number. The SPT number can be used as an empiricameasure of the compactness of the sand.

RESULTS AND DISCUSSIONS

The results of the study were presented as SoundingCurves, Histograms, Geoelectric sections, Maps, and

Logs.

Characteristic of the VES curves

Curves types identified ranges from A, KH and KHKvarying between three to five geoelectric layers. The KHcurve type dominates (Figure 2), constituting 62.5% othe totals while the A and KHK types constitute 25 and12.5% respectively. Typical curve types in the area areas shown in Figure 3a-c.


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0

10

20

30

40

50

60

70

A KH KHK

Curve Type

Frequency(%)

Figure 2. Histogram of the VES curve types in thestudy area.

Geoelectric and lithological characteristic

The VES interpretation results were used to prepare 2-Dgeoelectric sections displayed in Figures 4 and 5. Thegeoelectric sections identified four geoelectric/geologicsubsurface layers comprising the clay/sandy clay topsoil(resistivity varies from 92 to 736 -m and thicknessranges from 0.5 to 1.5 m); clayey coarse sand/laterite(resistivity varies from 925 to 3613 -m and thicknessranges from 1.2 to 19.5 m); clayey sand (resistivity variesfrom 576 to 1601 -m and thickness ranges from 5.4 to24 m) and coarse sand with resistivity varies from 3818 to

25839 -m.

Isoresistivity and isopach map of the topsoil

Figures 6 and 7 show the isoresistivity and Isopach mapof the topsoil respectively. The topsoil consists of clayand sandy clay. The south eastern parts of the area have

the highest resistivity value reaching 850 -m. The southwestern and north western areas shows relatively low

resistivity values (< 150 -m) indicating that, the westernparts have larger clay content than the eastern parts ofthe area. Figure 7 shows the Isopach map of the topsoil.The thickness of the topsoil ranges from 0.5 1.5 m.

Towards the south eastern parts of the area we have aclosure of highest thickness up to 2 m. The thickness ofthe topsoil is not important for the earthling electrodesystem since the burial of the electrode is meant to bewithin 5 - 8 m.

Isoresitivity and isopach map of the second layer

Figures 8 and 9 show the Isoresistivity and Isopach mapof the second layer respectively. The second layer com-prises of laterite and clayey coarse sand with resistivity

values ranging from 1000 to 5500 -m (Figure 8). Thethickness range from 2 to 19 m (Figure 9), as shown onthe Isoresistivity map. The highest resistivity valueswereidentified towards the south eastern flank of the studyarea (up to 5500 -m) and the lowest resistivity valueswere identified at the western flank( 1000 -m). The

Isopach map shows the largest thickness at the westernflank of the study area with a thickness up to 19 m. Thesecond layer can be considered as a possible candidatefor the burial of the earthing material as a result of itsappreciable thickness (up to19 m in western parts). Thehigher resistivity value of the second layer (sand layer) isnot suitable to

Figures 8 and 9 show the Isoresistivity and Isopachmap of the second layer respectively. The second layecomprises of laterite and clayey coarse sand with resis-

tivity values ranging from 1000 to 5500 -m (Figure 8)The thickness range from 2 to 19 m (Figure 9), as shownon the Isoresistivity map. The highest resistivity values

effectively serve as a medium for an earthing sys-temTherefore, there is need to increase the subsurfaceconductivity of this layer, especially within the area wherethe earthing electrode will be buried, preferably in thewestern parts of the area.

Geotechnical results

The borehole log (Figure 10) as well as the Conepenetration test plots (Figure 11), indicate that, the sub-soils are a consolidated reddish brown lateritic clayey andsilty sand mixture with varying silt content. Based on thesoil properties (identified from the collected soil samples)

a 3-layered generalized profile was compiled (Table 1)The top layer, which is about 0.5 m thick, consists ofconsolidated reddish brown lateritic clayey and silty sandwith vegetation roots. This top layer is underlain by a 29m thick layer of reddish brown lateritic clay, silt and fine tomedium grained sand mixtures, which are characterizedby high plasticity. Due to the observed variations in thesoil parameters, the subsurface can then be sub-divideinto two layers. The thickness of the top layer variesbetween 0.5 to 8.5 m, and the silt content increases withdepth, while the clay content decreases slightly. Thevalues of the Standard Penetration Test (SPT) increasesfrom 5 to 14 with a CPT of between 1 and 4 MPa (Table1). The thicknesses of the lower layer vary from 8.5 to 20m, and silt content decrease with depth as well as theclay content. The SPT-N values increases from 16 to 25and CPT from 4 to 10 MPa with an average of about 5MPa (Table 1).

Sub-soil engineering evaluation of the study area

Soil corrosion that can lead to severe corrosion failure isknown to be associated with low resistivity. Low resis-tivities (


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(a)

(b)

(c)

Figure 3. Typical sounding curves in the study area (a) KH Type, (b) A Type and (c) KHK Type.


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20

10

BH 1 VES 11 VES10 VES 1 BH 2

925

5334

1299

990

3613

1093

7539

16257

Clay

Coarse sand

Clayey Sand

Sand

0

10 m

25 m

Scale

N S22492 103

DEPTH(m)

30

0

BH Borehole

Figure 4. Geoelectric Section along North South.

25839

8253

6879

3818

7539

576 1542 16011556

1093

26352905 2170

27693613

VES 5 VES 4 VES 3 VES 2VES 1

20

10

0

10 m

25 mScale

E W

DEPTH

(m)

223 633736

571 224

30

Clay

Coarse sand

Clayey Sand

Sand

BH Borehole

0

Figure 5. Geoelectric Section along East West.


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787460 787480 787500 787520 787540 787560 787580 787600 787620

711120

711140

711160

711180

711200

711220

711240

711260

VES Stations

50 ohm-m

100 ohm-m

150 ohm-m

200 ohm-m

250 ohm-m

300 ohm-m

350 ohm-m

400 ohm-m

450 ohm-m

500 ohm-m

550 ohm-m

600 ohm-m

650 ohm-m

700 ohm-m

750 ohm-m

800 ohm-m

Contour line with value

0 m 25 m 50 m

150

Figure 6. Iso-resistivity Map of the Topsoil (First Layer).

787460 787480 787500 787520 787540 787560 787580 787600 787620

711120

711140

711160

711180

711200

711220

711240

711260

VES Stations

0.3 m

0.4 m

0.5 m

0.6 m

0.7 m

0.8 m

0.9 m

1.0 m

1.1 m

1.2 m

1.3 m

1.4 m

1.5 m

1.6 m

1.0 Contour line with value

0 m 25 m 50 m

Figure 7. Iso-pach Map of the Topsoil (First Layer).


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VES Stations

500 Ohm-m

1000 Ohm-m

1500 Ohm-m

2000 Ohm-m

2500 Ohm-m

3000 Ohm-m

3500 Ohm-m

4000 Ohm-m

4500 Ohm-m

5000 Ohm-m

5500 Ohm-m

6000 Ohm-m

787460 787480 787500 787520 787540 787560 787580 787600 787620

711120

711140

711160

711180

711200

711220

711240

711260

1500 Contour line with value

Figure 8. Iso-resistivity Map of the Second Layer.

787460 787480 787500 787520 787540 787560 787580 787600 787620

711120

711140

711160

711180

711200

711220

711240

711260

VESStations

1.0 m

2.0 m

3.0 m

4.0 m

5.0 m

6.0 m

7.0 m

8.0 m

9.0 m

10.0 m

11.0 m

12.0 m

13.0 m

14.0 m

15.0 m

16.0 m

17.0 m

18.0 m

19.0 m

0 m 25 m 50 m

1500 Contour line with value

Figure 9. Iso-pach Map of the Second Layer.


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0

5

10

15

20

5

6

6

7

8

12

15

16

18

19

20

21

21

DRILLING METHOD: SHELL & AUGER

SAMPLING METHOD: U2 & SPT

BORING NO: 1

BLOW COUNT/0.3 M

SAMPLE NO/DEPTH (M)

20.0

18.0

16.5

15.0

13.5

12.0

10.5

9.0

7.5

6.0

4.5

3.0

1.5

SURFACE CONDITIONS: COVERED WITH GRASSES & MODERATELY LEVELLED

SOILGRAPH

SC/SM

CH/SM

Grading Very Stiff

Medium stiff reddish brownlateritic silty clayey fine to

medium sand

Stiff reddish brown lateriticclay, silts, fine to

medium sand mixture

0

5

10

15

20

4

6

7

8

9

11

14

15

15

17

18

19

21



BORING NO: 2

BLOW COUNT/0.3 M

SAMPLE NO/DEPTH (M)

20.0

18.0

16.5

15.0

13.5

12.0

10.5

9.0

7.5

6.0

4.5

3.0

1.5


SOILGRAPH

SC/SM

CH/SM

Grading Very Stiff

Medium stiff reddish brownateritic silty clayey fine tomedium sand

Stiff reddish brown lateriticclay, silts, fine to mediumsand mixture

Borehole 1 Borehole 2

0

5

10

15

20

5

8

9

11

12

15

16

19

19

20

20

20

25



BORING NO: 3

BLOW COUNT/0.3 M

SAMPLE NO/DEPTH (M)

20.0

18.0

16.5

15.0

13.5

12.0

10.5

9.0

7.5

6.0

4.5

3.0

1.5


SOILGRAPH

SC/SM

CH/ML

Grading Very Stiff

Medium stiff reddish brownateritic silty clayey fine tomedium sand

Stiff reddish brown lateriticclay, silts, fine to mediumsand mixture

Grading with Coarse Sand

Borehole 3

Figure 10. Borehole Lithological Log Boreholes 1, 2 and 3.


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0

5

10

15

20

0 5 10 15 20

SLEEVE RESISTANCE IN M Pa * 10-1 CONE RESISTANCE IN MP a

DEPTHINMETERS

conesleeve

0

5

10

15

20

0 5 10 15 20

SLEEVE RESISTAN CE IN MPa * 10-1 CONE RESISTANCE IN MPa

DEPTHINMETE

ConeSleeve

CPT1 CPT2

0

5

10

15

20

0 5 10 15 20

SLEEVE RESISTANCE IN MPa * 10-1 CONE RESISTANCE IN MPa

Cone

Sleeve

0

5

10

15

20

0 5 10 15 20

SLEEVE RESISTANCE IN MPa * 10-1 CONE RESISTANCE IN MPa

Cone

Sleeve

CPT3 CPT4

0

5

10

15

20

0 5 10 15 20

SLEEVERESISTANCE IN MPa * 10 -1 CONE RESISTANCE IN MPa

Cone

Sleeve

0

5

10

15

20

0 5 10 15 20

SLEEVERESISTANCE IN MPa * 10-1 CONERESISTANCE IN MPa

Cone

Sleeve

CPT5 CPT6

Figure 11. Graph of the Cone Resistance Test Points (CPT1-6) within the study area.


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Table 1. Generalized sub-soil profile.

Layer No. Layer Thickness (m) Description of soil type and symbolCPT (MPa) SPT

N-values

1 0.5Topsoil; medium reddish brown lateritic clayey andsilty sand with vegetation roots (SC/SM)

2 8.0 Stiff reddish brown lateritic clay, silt and fine tomedium sand mixture (CH/SM) 5 to 12 (1 to 4 MPa)

3 11.5Stiff reddish brown lateritic clay, silt and fine tomedium sand mixture (CH/SM)

16 to 25 (4 to 10 MPa)

Table 2. Classification of Soil Resistivity in terms of the Corrosivity (Baeckmann andSchweak, 1975; Agunloye, 1984).

Soil resistivity (ohm-m) Soil corrosivity

UP to 10 Very Strongly Corrosive (VSC)

10 60 Moderate Corrosive (MC)

60 180 Slightly Corrosive (SC)180 and Above Practically Non- Corrosive (PNC)

electrolyte saturating or high concentration of dissolvedsalts in soil. Soil resistivity can therefore be classified interms of the degree of soil corrosivity as shown in Table 2.

The topsoil in the study area varies from slightlycorrosive to practically Non-corrosive (100 to 850 -m)(Figure 6), while the second layer is practically non-corrosive (1000 to 5500 -m) (Figure 8). Any metal orsteel structures within the area are practically notexposed due to chemical corrosion. The earth medium(usually clayey) must have high electrical conductivity orlow electrical resistivity. Clays are characterized byresistivity values in the 1 to 100 -m range. Thesubsurface (at depths of 1 to 5 m) within which theelectrical materials could be earthed have resistivity

values varying from 1000 to 5500 -m (Figure 8). Thesesandy soils are a poor medium to act as an earth. Aconductive earth medium will have to be created by usingclay or salt (brine) chambers within the survey site.The result of the sub-soil geotechnical investigationindicates that, the site is underlain by a layer of mediumstiff-to-stiff lateritic clay and silty sand to a depth of 20 m.The choice of foundation must take into account the

collapsible characteristics of the clay material. Apart from0.5 m of the topsoil, the overburden soil consists primarilyof reddish brown lateritic clay, silt and fine to mediumsand mixtures. The soil classification results indicatethatthe upper 8 m of the overburden soil contains moreclay with an average cone resistance of about 2 MPa(Table 1). The lower layer consists of reddish brownlateritic soil to the depth of 20 m, but with less clay andmore silt. The cone resistance of the lower layer variesbetween 4 to 10 MPa (Table 1). The foundation of theproposed structure can be established in this layer for the

support of the proposed structure.

Conclusions

An integrated geophysical and geotechnical investigationwas carried out at the proposed switch station for atelecommunication mast at a site in the south easternparts of Nigeria. The geophysical survey employed thevertical electrical sounding technique using schlumbergeconfiguration. A total of sixteen (16) sounding wereconducted. The geotechnical aspect involved the drillingof three (3) Boreholes at locations strategically distributedwithin the survey site. Six (6) Cone Penetration Tespoints were occupied within the area to investigate the in-situ strength properties of the soil. Although CPT provides valuable information, this information is restricted tothe location of the measurement. The results of thegeotechnical survey were used to control the geophysicainterpretations.

The geophysical results show four layers within thestudy area. These include the topsoil (Mixture of sand, sil

and clay), lateritic clayey with coarse sand, lateritic clayeyand sand. The second layer is supposed to accommodate

the earthing electrode is resistive; hence, there is aneed to enhance the conductivity of this medium. Anyearthing materials buried in a resistive medium may notprotect the instrumentation when there is a lighting orthunder-storm. The results of the geophysical investiga-tion also show that, the study area are generally of moderate resistivity value (>180 -m), hence any protectedsteel or metal structure buried within this area may not beaffected by chemical corrosion.


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The results of the geotechnical investigation show thatthe site is underlain by layers of medium stiff-to-stiff late-ritic clay and silty sand to the depth of 20 m. The choiceof foundation material must take into account the charac-teristics of the clayey material.

REFERENCES

Agunloye O (1984). Soil aggressivity along steel pipeline route atAjaokuta. J. Mining Geol. 21(1 & 2): 97-101.

Avbovbo AA (1978). Tertiary lithostratigraphy of Niger Delta: Am. Assoc.Pet. Geol. Bull. 62: 295-300.

Baeckmann WV, Schweak W (1976). Handbook of cathodic protection:The theory and practice of electrochemical corrosion protectiontechniques. Portucullis press survey. p. 396.

Baldi G, Bellotti R, Ghionna VN, Lo Presti DCF (1995). Modulus ofsands from CPT and DMT: Proceedings of the 12

thInternational

Conference on Soil Mechanics and Foundation Engineering, pp.165170.

Bremmer CN (1999). Developments in geomechanical research foinfrastructural projects, in 12th European Conference on SoiMechanic and Geotechnical Engineering: Geotechniek, Special Issuepp. 5255.

Eslaamizaad S, Robertson PK (1998). Cone penetration resistance osand from seismic tests, in Robertson PK, Mayne PW, Eds.Geotechnical site characterization: Balkema, pp. 10271032.

Ibe AC (1988). Coastaline erosion in Nigeria. Ibadan university press

Ibadan, Nigeria.Vander Velper BPA. (1988). Resist version 1.0, Msc. Research project

ITC, Delf Netherland.

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Akintorinwa and Adesoji

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